Suede- or nubuck-type leathery sheet like articles produced by raising, with sandpaper or the like, the surface of a sheet like article made of a fibrous base material made mainly of a fabric such as nonwoven fabric and polyurethane resin have appearance and surface characteristics resembling natural leather and also have excellent features such as uniformity, dyed color fastness, that are not found in natural leather, thus serving widely not only for clothing, but also for the coverings of furniture such as sofas, coverings of car interior materials, and other similar materials to be used for a long period of 5 to 10 years.
The properties of such a sheet like material can be designed widely by appropriately combining a fiber-made base material and a polyurethane resin.
For example, there is a proposal for using a polyurethane resin composed mainly of polytetramethylene glycol, an organic diisocyanate, and a glycol chain extender to produce a leather like sheet material having a very soft texture that is comparable to high grade wool fabrics used for business suits or the like (see Japanese Unexamined Patent Publication (Kokai) No. SHO 59-192779). However, polyether based polyurethane resins produced from polytetramethylene glycol tend to be easily degraded by ultraviolet rays and heat, and this may cause pilling on the surface during use or cause fibers to come off, resulting in the problem of the incapability of standing up to long term use. Polyester based polyurethane resin is also a polyurethane resin frequently used for production of leathery sheet like materials. It is highly light resistant against ultraviolet rays, for example, but suffers easily from degradation due to hydrolysis of ester bonds, leading to similar problems including generation of surface pilling and fibers coming-off during long term use.
To solve these problems, polycarbonate polyol based polyurethane resins have been used as resin components to impregnate fibrous base materials for use in leathery sheet like articles to serve for applications for automobile interior finishing, particularly those requiring durability.
For example, there is a proposal for using polycarbonate based polyurethane resin produced by reaction of a polycarbonate polyol, an alicyclic polyisocyanate, and an aromatic polyisocyanate (see Japanese Unexamined Patent Publication (Kokai) No. HEI 3-244619). When adopted as a resin component to impregnate a nonwoven fabric of ultrafine fibers, however, the use of a polycarbonate based polyurethane resin based on a polyhexamethylene carbonate results in a sheet like article with a plastic like texture and coarse touch. When surface fibers are raised with sand paper, in particular, the polyurethane resin can become too stiff and form a coarse surface with short raised fibers, possibly leading to a great difficulty in realizing a high quality product with elegant raised fibers.
In addition, it has been reported that a specific type of aqueous polyurethane resins serve to produce an artificial leather that has an improved processing yield and heat resistance that enables long term continuous operation of the dyeing machine, and a polycarbonate based polyurethane has been proposed as such a specific aqueous polyurethane (Japanese Unexamined Patent Publication (Kokai) No. HEI 11-81156). However, the leathery sheet like article disclosed in that proposal is extremely low in polyurethane content and raised surface fibers can come off to cause a large change in appearance when used for a long term, possibly leading to an extreme case where the woven fabric reinforcing material is exposed from the surface. When a raised fiber type leathery sheet like article is produced by using such an aqueous polyurethane resin, an increased addition of polyurethane resin aiming to improve durability can cause extreme shortening of raised fibers or stiffening of the texture even when it is a slight increase. Thus, it is difficult to produce a leathery sheet like article that is high in both flexibility and durability.
Thus, it could be helpful to provide a sheet like article having elegant surface quality with uniform appearance, flexible and highly crease recoverable texture, and high resistance to light and hydrolysis.